1. Field of the Invention
The present invention relates to an information processing device that transmits print data to a printing device such as a printer, a print data transmission method, a print data transmitting program, and a recording medium.
The present invention also relates to a printing device that prints out the print data transmitted from the information processing device, and a printing method that is performed by the printing device.
2. Description of the Related Art
As network data transmission has been rapidly developed and is now widely used, more attention has been drawn to encryption techniques for transmitting data securely over a network, as is disclosed in Japanese Laid-Open Patent Application No. 2001-211148. By encrypting data prior to transmission, the original plain text can be prevented from being transmitted over the network, and it becomes difficult for an ill-mannered user to gain access by performing wire tapping or the like.
When document data are printed out, the same problem as the above occurs in transmitting the print data from a device such as a personal computer (PC) to a printer. There is a possibility that the print data that are being transmitted from the PC might be wrongfully intercepted and sent to a printer that is not the originally selected printer. To counter this problem, the print data should be encrypted in the PC; and the encrypted print data are transmitted to the printer. Such a printing system can give more security to data transmission.
The encryption techniques can be roughly divided into common key encryption (symmetrical key encryption) methods and public key encryption (asymmetrical key encryption) methods. The former methods include DES and RC4 in which the same key is used for encryption and decryption. The latter methods include RSA in which a public key and a private key are used, and the encryption key and the decryption key are different.
By any of the common key decryption methods, however, encrypted data can be easily decrypted, once the decryption key is stolen. Therefore, the management and delivery of the encryption key become very important. By any of the public key decryption methods, on the other hand, only the public key is delivered to the receiving end, and the private key need not be delivered. Accordingly, a public key encryption method is safer than a common key encryption method. With a public key encryption method, however, there are drawbacks that it is necessary to employ a complicated mechanism to perform bidirectional communication between a PC and a printer, and that the operation speed is low as a large amount of arithmetic operations is involved in encryption and decryption.
Therefore, a common key encryption method is considered to be more suitable for the above described printing system, because of its readiness for mounting and greater processing capacity.
By a common key encryption method, however, it is necessary to use the same key at both the encrypting side and the decrypting side. Therefore, the encryption key as well as encrypted print data need to be transmitted from the encrypting side to the decrypting side, or identical keys should be stored in advance on both sides.
In the former case, the encryption key might be easily stolen, in which case the encryption of print data becomes pointless.
In the latter case, the possibility of the encryption key being stolen is reduced. However, if there are two or more printers with the same encryption keys, print data can be decrypted by any of these printers including one that is not the selected printer.